More local history – the lime kiln

I’ve occasionally written about getting out and about and exploring local history, here in the southeastern part of the Province of Ontario. This is something I should probably be doing more of – along with writing about it here. But with the riotous colours of the fall trees already a memory, and bleak and bleary early-winter weather settling in, it’s getting a little harder to find the motivation.

Fortunately, I can turn my memory back to a trip to the Mountsberg Conservation Area on labour day weekend, which yielded yet another unexpected excursion into Ontario’s not-so-recent past. Along with the excellent Raptor Centre, which I’ve mentioned before, this sprawling site includes 16 kilometres of trails, just perfect for a hike in the crisp fall air. One of them, the Pioneer Creek Trail, turned out to include that tumble-down ring of rocks in the photograph above. Although it may look like a stone-age hut circle, it’s actually the remains of a lime kiln, designed for baking limestone into quicklime. In the 1800’s, cooking up limestone was apparently a fairly common local industry.

According to Natural Resources Canada, limestone is still mined and processed today in 119 locations across the country, by 86 companies, although some of these are related to each other. The vast majority are in the central provinces of Ontario and Quebec, although there is a scattering in other places, from the west coast of British Columbia all the way to Newfoundland and Labrador on the east. Almost all are conventional quarries, with a couple of open-pit mines thrown in, although I confess I’m not sure quite what the difference is.

Limestone is a fascinating substance. It’s sedimentary, easily fragmenting into layers. If you’ve ever driven through a highway cutting in limestone bedrock, you’ll have seen these layers easily. In this part of the world, it’s a result of deposition from an ancient, shallow tropical sea from early Paleozoic times, mainly of Middle Ordovician age, meaning something like 450 million years ago. It in turn covers a much older, and harder formation called the Frontenac Arch, which is Precambrian. There’s an extensive discussion of this geological history here, for those interested.

Limestone is made mainly of calcium carbonate, in the forms of calcite and aragonite, and is often almost completely comprised of fossilized skeletons of tiny organisms – corals, and foraminifera, which are tiny creatures usually found in the ocean. There’s so much of it about that my home town of Kingston, nestled at the beginning of the Saint Lawrence River at the eastern end of Lake Ontario, is known as the Limestone City. There, it was used extensively for building; in other parts of the Ottawa Valley, its derivative, quicklime, was used in mortar, plaster, and whitewash. I’m presuming that its uses here, a little bit farther west, were similar.

Which brings us back to that lime kiln. The chemical process of calcination – from the latin Calcinare, “burning of lime” – is pretty straightforward. Calcium carbonate breaks down to calcium oxide, better known as quicklime, and gives off carbon dioxide. The amount of heat required is fairly extreme – more than 825 Celsius. That’s hot enough to melt aluminum (660 Celsius) and nearly hot enough to melt brass (930) or silver (961). By comparison, a candle flame is about 1,000 Celsius; a blowtorch might be 1,300. A hot restaurant pizza oven might be only 350 or so.

That’s a lot of heat, so I suspect these things needed tending round-the-clock to keep them stoked up and cooking hot enough. I can imagine diligent workers gathered night-long, an additional fire going to keep them warm and dissuade the inevitable legions of mosquitoes. It evokes memories of the charcoal burners that I recall from the Arthur Ransome book, Swallowdale, which I read years ago. And it makes me remember picking up flakes of mica from the remains of open pit mines near my parents’ cottage, another of southeastern Ontario’s long-gone industries. Perhaps that’s worthy of another investigation, once winter gets out of the way.

About Richard Wintle

I am Canadian by heritage, and a molecular biologist and human geneticist by training. My day job is Assistant Director of a large genome centre, where I do various things along the lines of "keeping the wheels on". In my spare time, I tend to run around with a camera, often chasing race cars, abandoned barns, and sundry wildlife.